Investigation of using positronium and its annihilation for hypoxia PET imaging

Positron emission tomography (PET) is widely used for medical imaging to investigate the spatial distribution of pharmaceuticals labelled with positron emitters in patients. This study investigated the potential to perform three gamma (3 gamma) imaging based on ortho-positronium annihilation for assessment of tumour hypoxia. Evaluation of Oxygen deficiency is necessary to assure successful treatment. It was reported that PET imaging with a radioisotope could be used as molecular markers to detect tumour hypoxia. This method is based on the physics of 2 gamma annihilation. However, the 3 gamma annihilation yield is governed by the positronium formation as well as in quenching rates which could be used as a new PET molecular imaging modality. This study provides a method for the preparation of biological samples with different oxygen concentrations as well as developing a configuration system for the determination of the 3 gamma yield using high-purity germanium (HPGe) detectors to investigate the measurement of 3 gamma imaging. This study compares the decay rates in oxygen and nitrogen saturated samples of water and serum, the results show that 3 gamma annihilation with different oxygen concentrations could illustrate the oxygenation in biological models. Even though many diverse disciplines are involved in this work, the advantages and disadvantages of each possible technique have yet to be concisely summarized. This study sets out the background to the clinical applications of the 3 gamma PET technique and compares this non-invasive method with existing oxygen measurement devices.